<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>三角形</title>
    <style>
        div {
            /* 把下、左、右三条边隐藏掉（颜色设为 transparent） */
            width: 0;
            height: 0;
            /* border-width: 300px;
            border-style: solid;
            border-color: pink transparent transparent transparent; */
            border: 300px solid transparent;
            /* border-top: 300px solid pink; */
            border-top-color: pink;
        }
    </style>
</head>

<body>
<div></div>
</body>

</html>